Telephone system



June 20, 1933. c, R BROOKS 1,914,357

TELEPHONE SYSTEM Original Filed Oct. 24, 1930 2 Sheets-Sheet l i.: ww :SS

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Q GWW June 20, 1933. Q R BROOKS 1,914,357

TELEPHONE SYSTEM Original Filed Oct. 24, 1930 2 Sheets-Sheet 2 Patented June 20, 1933 rarer CHARLES R. BROOKS, OF CHICAGO, ILLINOIS, ASSXGNOR, BY MESNE ASSIGNMENTS, TO

ASSOCIATED ELECTRIC LABORATORIES, INC., GF CHTCAGO, LLNOIS, A CORPORA- TION OF DELAWARE TELEPHONE SYSTEM Application filed October 24, 1930, Serial No. 490,877. Renewed November 17, 1932.

The present invention relates to telephone systems in general, but is concerned more particularly with automatic telephone systems used to give service to subscribers in towns and villages and in the surrounding rural districts.

rlhe principal object of the present invention is the production of new and improved circuit arrangements for enabling satisfactory automatic telephone service to be given to the rural lines entering a town or village exchange, even though many of the rural lines have a high resistance and be in a relatively poor state of repair'.

vt is common knowledge that vrural telephone lines are often several miles in lengt-h and that they are especially liable to becoming partially grounded at rather irequent intervals when, for example, they come in Contact with growing trees and other conductive objects. The control of automatic switches from substations on rural lines, therefore, has long been recognized as quite a diliicult problem. About the mostnearly satisfactory solution of the problem heretofore advanced has been the use of the so-called simplex-dialling arrangement, according to which a dialling circuit used both sides of the line in parallel with a ground return. Such'a simplex-dialling arrangement is disclosed in the Patent 1,686,- 879, granted October 9, 1928, to Norman H. Saunders. This proposed solution, however, is open to the objection that the simplexdialling rural lines must be placed in a reasonably good state of repair, and must be grouped separately from the loop-dialling village or town lines, on account of the dif- Jferent dialling circuit; and the simplex-dialling arrangement is, of course, not appli cable to single-wire rural lines employing the earth as a return conductor in the talking circuit. And there are many such lines in use today.

The control of the operation of automatic switches over a single-wire ground-return rural line has heretofore proved to be impractical when the controlling current source` is located at the exchange. lt is, accordingly, an object of the invention to produce a new and improved control circuit especially suitable for single-wire rural vtelephone lines, wherein the current source for the control circuit is located at the subscribers substation rather than at the eX- change.

lt is a further object to provide suitable receiving apparatus in the automatic exchange to respond to the controlling impulses transmitted from the current source at the subscribers substation and in turn operate the automatic switches.

A feature of the present invention is that each singleavire rural line is provided with an individual repeater which responds to the impulses received from the rural line and repeats standard loop impulses to the automatic switches.

lt is a further feature of the present invention that ringing current is applied to acalled rural line from the impulse repeater by means of a ringing relay, which is, in turn, controlled fromthe connector used to extend the connection to the line, and in` accordance with the code of the desired subscriber on the called line. A special feature of the individual-line repeater is that it may be used equally well with single-conduc tor lines and two-conductor lines.

Other objects and features of the invention will appear upon a further perusal of the specification in connection with the accompanying drawings comprising Figs. l and 2, which show by means of the usual circuit diagrams-a suliicient amount of equipment in a telephone system embodying the `features of the invention toenable the invention to be understood.

F ig. l shows a rural single-conductor party line l0 and one of the substations, Al, thereon; together with the repeater R in the exchange, individual to the party line l0.

Fig. 2, which should be placed to the right of Fig. l, with the corresponding conductors at the edges of the sheets in alignment, shows automatic switching apparatus that may be used in setting up connections to and from the party'line l() of Fig. l. The lineswitch LS may be the same as the lineswitch LS1 in Fig. 2 oi the hereinbetore-mentioned Saunders Patent 1,686,87 9, except for the addition of a grounded back contact tothe lower armature of relay 201 in the Saunders patent so as to enable line relay 202 to operate over the loop circuit; and the lineswitch LS is, therefore, a regular two-wire rotary lineswitch. The selector S, of which only the wipers are shown, may be any standard two-wire selector, being mechanically of the type having the bank contacts arranged in horizontal rows or levels.

The connector C1 is of the same mechanical type as the selector S, and it may be the same as the connector C1 in Fig. 3 of the said Saunders Patent 1,686,879, except that relay 301 of the connector C1 in the present drawings is arranged to operate over Va loop circuit when the 'called subscriber responds, as is'shown in the present drawings; and the ringing current is supplied to the called line in the present connector over the lower line wiper instead of over the upper line wiper in the Saunders patent. The parts of the connector C1 and the code selector CS which are not shown in the present drawings may be the same as the corresponding parts in the Saunders patent. rlhe connector C1 has access toa number ofcommon battery lines, such as the line of substation A2, and it has access to a number of local-battery rural lines, such as theline 10 of substation A1, Fig. 1. Y

@all from substation A1 to substation A2 The invention having been' described generally, a detailed description of the operation of the apparatus shown will now be given. For this purpose a call from substation Al of Fig. 1 to substation A2 of Fig. 2 will now be explained. n

In order to condition the automatic switching apparatus to be controlled by the calling device CD, the subscriber at substation A1 operates his hand generator 9 to project ringing current over line 10 to the repeater R. 'lhe AC relay 22, in series with the associated condenser, is normally connected between line l() and ground at terminal 32. This alternating-current relay 22 is of a familiar type, having a laminated core provided with a winding, with the upper end of the core divided into two sections, one of which is provided with a copper collar in order to secure a suflicient magnetic lag, a phase displacement, to cause the armature to remain attracted throughout the entire application of ringing current. lVhen relay 22 responds to the ringing current, it closes a circuit for the slowacting relay 23, whereupon relay 23 operates and repares a circuit for relay 25. At its mid le lower armature, relay 23 places ground on the start conductor, which is common to all of the repeaters such as R, starting the 100G-cycle oscillator 0S into operation, and closing a circuit for relay 41. Relay 41 operates and applies commercial power to the primary winding of the stepdown transformer 42, which is usedv to provide vfilament current for the vacuum tubes 34 and 35. At its lower armature, relay 23 closes a filament-lighting circuit for the tubes 34 and 35, enabling the filaments of these tubes to become lighted. WVhen the application of ringing current to line 10 ceases, the AC relay 22 falls back and operates relay 25 through contacts of relay 23. WVhen relay 25 operates, it closes a circuit for the slow-acting relay 24. Relay 24 operates. A moment later, relay 23 falls back because its circuit is now opened at the contacts of relay 22, and it opens the circuit of relay 25. Relay 25 is provided with a weighted armature spring, and this armature spring vibrates back and forth for sev;v eral seconds, closing a circuit for relay 24 through the inner lower armature of relay 24 at the limit of each stroke. Relay 24 is thus held operated as long as to weighted armature spring relay 25 is vibrating with substantial amplitude, giving the subscriber at substation A1 time to remove his receiver and establish a holding circuit for relay 24 to be hereinafterexplained.

As a result of its operation, relay 24-at armature 31 and at its lower armatureshunts the Vcorresponding contacts of relay 23 so as to maintain the oscillator in operation and to maintain kthe ilaments of tubes 34 and 35 lighted. Consequently, as soon as relay 23 falls back, plate current from batery 48-and through the inner lower armgature of relay 23 and armature 30-in the plate circuits of tubes 34 and 35; the limiting resistance 44 being included in the plate circuit of tube 34, while relay 26 is included in the plate circuit of relay 25. By the proper adjustment of the potential of the grid-biasing battery 49, however, and by the proper adjustment of the potential of the 100G-cycle current impressed on the grid element of tube 35 by the oscillator OS, through the interposition of transformer 46, the normal iiow of plate current through the relay 26 is of a value somewhat below that required to operate the relay. Relay 26, therefore, does not operate for the present.

As a further result of the operation of relay 24, the line 1() is extended through contacts of relay 21 and through the upper contacts of relay 24 to the grid element of the vacuum tube 34, so as to bring the tube 34 under the control of the calling line. The grid-leak resistance 43 is provided in conjunction with the individual-biasing battery shown connected in series with the conductor leading to the tube 34, in order to permit the desired normal flow of plate current through the plate circuit of the tube.

After operating the hand generator 9, the

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subscriber at subst-ation A1 removes his receiver 5, whereupon current from the transmitter battery 4l starts to flow through the lower winding of the induction coil 6 and through the transmitter 7. At the same time, a negative potential is impressed on the line 10 from the transmitter battery e through the switchhook contacts and the receiver 5, by way of the secondary winding of the induction coil 6 and the impulse contacts of the calling device Cl), rllhis results in a small Acurrent flow through contacts' of the unoperated 'relay' 21 and contacts of the operated relay 24 to ground by way of the grid-leak resistance 43. rlhe drop across the liiglrresistance element .43 is very nearly equal to the total potential of the transmitter battery Ll; and, as a result, the grid of the vacuum tube 34 is suddenly r ndered about four and one-half volts more negative than it was before the removal of the receiver. is a result, there is a sharp reduction in the current flow through the plate of the tube 3e and limiting resistance causing an impulse to be transmitted through the condenser to the grid element of the vacuum tube 35 by way of the secondary winding of the transformer 46. Since this impulse is occasioned by a lessening of the flow of current from the positive erminal of the plate battery 48, it is of a positive polarity, causing a. momentary increase inthe flow of plate vcurrent through the plate-iilain'ent circuit of the tube 35 by way of the plate relay 26. As a result, relay 26 operates, and it remains operated even after the impulse subsides because the normal flow of plate current Yis sufficient to hold it operated once it has been operated. rt its upper armature, relay 26 connects. the line 10 through to the left-hand repeatingcoil windings in order to prepare the coinplete talking circuit; and, at its inner con taots, relay 26 connects up conductor 50 to right-hand repeating-coil windings, thereby closing a direct-current bridge across conductors and 52 by way of the right-hand repeating-coil windings, the upper winding of relay 27, and contacts of relay 27. As a result, relay 27 operates in series with the line relay (not shown) of the lineswitch LS, and this line relay operates and applies ground potential to the private-normal conductor 51, as in the case of the line relay 201 of the Saunders patent hereinbefore referred to. llfhenrelay 27 of the repeater lt operates, it closes a locking circuit for its lower winding at its inner lower armature to the now-grounded conductor 51; and at its upper armature it replaces its own upper winding by the associated rresistance element, which is thereby connected across the condenser associated with the right-hand repeating-coil windings.V At its lower armature, relay 27 disconnects relay 28 from conductor 51, and connects conductor 51 to the winding of relay 2i, thereby completing a holding cir cuit for relay 24. This holding circuit is established, it will be understood, before the weighted armature spring of relay 25 has ceased to vibrate. Relay 28 is rendered slightly slow to operate by the copper collar on the armature end thereof-as indi cated by the solid-black upper portion of the relaywhich prevents relay 28 from operating over conductor 51 before it is disconnected.

Responsive to the above-mentioned oper ation of the line relay thereof, lineswitch LS of Fig. 2 is operated in the usual manner to hunt for and seize an idle selector. lt will be assumed that the selector S is the first one found to be idle and is there fore seized. Upon being seized, the Selector S is prepared for operation in the usual manner, conductors 50 to 52 being extended through to the selector S by the operation of the lineswitch LS. The line and release relays (not shown) of the selector S are now operated, and the release relay is main taining ground potential on conductor 51.

After removing his receiver, the subscriber at substation A1 manipulates his calling device in accordance with the digits in the desired number. Upon the return of the calling device CD to normal after its ma# nipulation in accordance with the first digit of the desired number, the impulse springs of the calling device are opened a number of times corresponding to the digit dialled. lVhile the calling device is in an olf-normal position, the receiver 5 and the upper wind# ing of the induction coil 6 are shunted in or der to provide a battery impulsing circuit, and in order to prevent the mild clicking which would otherwise be heard in the receiver 5.

Each time the impulse springs of the calling device CD are opened, the additional negative potential that Was applied initially to the grid of the tube 34 upon the removal of the receiver at substation A1 is abruptly removed, whereupon the plate current through the tube 34 is increased. The increase of the plate current, of course, is brought about by the lowering of the ef fective plate-lament resistance of the tube 34, with the result that a negative impulse is transmitted to the grid of tube 35, through condenser 45, and the upper winding of transformer i6. This results in a momentary lowering of the current-flow through the plate circuit of tube 35 and through plate relay 26, whereupon relay 26 falls back. As mentioned before, the normal flow of plate current through tube 26 isl such that the relay remains unoperated when it isin an unoperated state. It has been found by experiment that relay 26 will' not i lowered in the manner just described. This is nov-doubt due to the slight tendency of thecore of relay 26 to actas a permanent magnet, .which effect would probably not be present if a laminated core or one of very l. soft iron were used.

A Each time the impulse springs of the calling device CD close, following an interruption in the line circuit, the additional negative potential is suddenly reapplied to the l. grid element of tube 34, whereupon a positive impulse is transmitted as hereinbefore explained from the plate element of tube 34 to the grid element of tube 35, by way of the condenser and the upper winding of transformery 46. When this occurs, the current flow in the plate circuit of tube 35 is momentarily increased, causing relay 26 to reoperate.

Theresult of the foregoingoperations is that relay 26 falls back each time the impulse springs of the calling device CD are separated, and the relay 26 reoperates again each time the impulse springs of the calling device4V CD close. By this operation, the digitfdialled by the calling subscriber is repeatedto the selector S, F ig. 2; and the line relay therein (not shown) operates just as ythough the calling device CD were connected directly in series with the line relay, in place of the inner contacts of relay 26. Responsive to the series of deenergizations of its linerelay, the selector S is operated to raiseits wipers step by step in the usual manner .until they come to rest opposite the desired level of bank contacts. Following this, the selector S searches for an idle connector in the desired level and extends the connection through to the first one found robe idle. Assuming that the connector C1 is the first one found to be' idle, line relay 302 therein is operated over the loop circuit including conductors and 52 when the connection is extended to the connector by way of the selector` S, and the connector is prepared for operation in the usual manner by the operation of the slow-acting release relay 303. Ground potential is now maintained on conductor 51 at the upper contacts of relay 303.

When the tens digit of the desirednumber is dialled, line relay 302 of the connector Cil responds, with the result that the wipers 310--312 of the connector are raised step by step until they come to rest opposite the desired level .of bank contacts.

Q When the units digit of the number Vis dialled, the connector Cl is controlled by theline relay 302 sothat it rotates its wipers 310-312 step by step over the contacts in the selected level until they come to restl Leiessv on the bank contacts assigned to the line of substation A2. If this line is idle, the connection is complete rthereto as described in the hereinbefore-mentioned patent to Saunders; but the connection is denied and busy tone is returned to the calling line in case the line is found to be busy. Assuming that the called line is found to be idle, the connection is made and the busy tone is not returned. In this case, the code selector CS responds to the final digit in the number and selects one of the associated code conductors to control the ringing relay 307. In case the line of substation A2 is an individual line, the final digit is ordinarily the digit l.

Following the dialling of the final digit, ringing relay 307 is controlled by the associated code generator and in accordance with the setting of the code selector CS to apply ringing current to the called line from the generator G2.

Vhen the subscriber at substation A2 responds to the ringing of his bell by remov ing his receiver, a direct-current bridge is closed across the conductors of his line, and back bridge relay 301 operates in series with the two conductors of the line during the silent interval. Upon operating, relay 301 closes a circuit (not shown) for releasing the code selector CS to terminate the ringing operation. Relay 301 also reverses the connections between the inner terminals of the left-hand repeating coil Vwindings and line relay 302, thereby reversing the direction of current flow in the incoming line conductors. This reversal of current liow has no particular effect at this time, but is used in many cases to give supervision in case an operator is calling, and to operate a message register and the like.

The calling and called subscribers may now converse with each other as desired, the transmitter at the calling station being energized, as before mentioned, by the battery 4; while the transmitter at the called station A2 is energized by the current flow through backbridge relay 301 in the connector C1.

After the conversation is terminated, the two subscribers replace their receivers. When the receiver is replaced at substation A2, back-bridge relay 301 falls back and reverses the current flow in the incoming I conductors to normal.

When the receiver is replaced at substation A1, the potential on the grid element of the tube 34 is rendered less negative, whereupon a` negative impulse is delivered momentarily to the grid element of the tube 35, as hereinbefore explained, to cause a momentarily lowering of the current in the plate circuit of the tube, causing relay 26 to fall back. Relay 26 now remains in normal position, and the line and release relays 302 and 303 of the connector C1 to both fall back. i Relay 303 removes ground from the associated release trunk-conductor.

@all from substation A2 to substation A] ln order to explain the operation of the system when a call is extended to the line 10, it will be assumed that the subscriber at substation A2 desires to converse with the subscriber at substation A1.

When the receiver is removed at substation A2, the lineswitch (not shown) individual to the substation A2, which may have its bank contacts connected in multiple with the back contacts of the lineswitch LS, operates over the conductors extended down at the lower right-hand corner of Fig. 2, and seizes an idle selector in the usual manner, the selector S, for example.

W'hen the first digit is dialled, the selector S operates in the usual manner to extend the connection to an idle connector, the connector C1, for example. ln the connector C1, the line and release relays A302 and 303 are operated as before describedto prepare the connector for operation, and the connector responds to the second and third digits in the desired number to position the wipers B10-312 of the banks contacts to which the "r.o1.nial7 conductors 50', 51, and 52 are connected. The usual busy test is made; and, if the line of substation A is idle, no ground potential is encountered on conductor 51', and ground potential is accordingly applied to this conductor through the test winding of the switching relay (not shown) of the connector C1 to conductor 51. When this occurs, the switching` relay of the connector C1 is operated to complete the connection t-o conductors 50-52, and to apply ground potential directly to conductor 51. As a result of the application of ground potential to conductor 51 by way of conductor 51, the switching relay of the lineswitch LS-corresponding to switching relay 201 of the lineswitch LS1 in Fig. 2 of the above-mentioned Saunders patentis operated part way, as explained therein, to disconnect the associated line relay and clear the conductors 50 and 52 of local attachments. At the same time., relay 28 of the repeater R operates from the ground potential on conductor 51 and through cont-acts of relay 27 and connects the ringing relay 21 of the repeater R to the negative talking conductor 50, in multiple with the upper winding of back-bridge relay 301 of the connector C1, preparatory to the ringing operation.

When the subscriber at substation A2 operates his calling device in accordance with the party-selecting digit in the number, the code selector CS associated with the connector C1 of Fig. 2, 'is operated to select the code assigned to substation A1, Fig. 1. When this occurs, the relay 307 is operated over the selected code conductor to send out the code assigned to substation A1. Each time relay 307 is operated, ringing current from the generator G2 is applied to wiper 312 and is sent out over conductor 52, to conductor 52, but this ringing current is of no utility in the present connection. As a further result of each of its operations, relay 307 disconnects the nega- 'ive line wiper 310 from the upper winding of relay 301 and connects it to ground. This is done to provide a return circuit the ringing current in the case of a connection to a regular common-battery substation, as, for example, the substation A2. In the present case, however, each application of ground potential to wiper 310 results in the closure of a circuit over conductors 50 and 50 for ringing relay 21 of the repeater R by way of contacts of relay 28. Each time relay 21 operates over this circuit, it projects Aringing current from the generator G1 over line 10. The code assigned to substation A1 is, accordingly, sent out on line 10. Each time it operates, relay 21 closes a circuit for relay 25 at its inner armature. Relay 25 operates responsive to the first operation of relay 21, and operates relay 24 to secure the performance of the hereinbefore-described operation ot starting up the oscillator OS and lighting the filaments of the tubes 3A and 25 preparatory to the cutting olf of the ringing current when the called subscriber responds. It will be noted that the Amiddle armature of relay 21 grounds the associated section of line 10 each time relay 21 operates. The middle armature makes contact before the upper armature leaves its normal position, and breaks contact only after the upper armature has returned to normal position. By this arrangement, line 10 is discharged after each application of ringing current has been made thereto, so as to prevent a momentary impulse received by the grid of the vacuum tube 34 as would happen, otherwise, in case a charge is left on the condensers associated with the ringer, such as the ringer 8 of substation A1.

As a result of the above-described energizations and deenergizations of relay 21 in accordance with the operations of the ringing relay S07 of the connector C1, Fig. 2, the ringers on the party line 10 are operated in accordance with the code of substation A1.` Relay 25 is `operated each time relay 21 operates,'and it is released each time relay 21 releases, with the result that it continues to vibrate and hold relay 24 operated for several seconds in case no further application of ringing current is received. In case the calledsubscriber at substation A1 does not respond the first time his code is sent out, the weighted armature spring of relay 25 continues to vibrate and hold relay 24 operated until the code is sent out the second time, and in case the subscriber at substation A1 does not answer after a reasonable time, and the connection is abandoned by thefsubscriber at substation A2-causing the release of the automatic switches-the relay 25 ceases to vibrate after a few seconds, and relay 24 falls back.

Assuming, however, that the subscriber at substation A responds after his code has been sent out one or more times, the removal of the receiver impresses the negative potential of the transmitter battery 4 on line 10. As a result, with relay 21 deenergized, the negative potential is added to the negative potential normally existing on the grid of the tube V34, causing a momentary positive impulse to be delivered-as hereinbefore described-,to the grid element of tube 35. This causes the described momentary increase of plate current and the consequent operation of plate relay 26. When relay 26 operates, it places the upper winding of relay 27 in a closed bridge of conductors 50 and 52, whereupon this relay operates in series with the windings of backbridge relay 301 of the connector C1 and locks itself to the grounded conductor 51, at the same time cutting out its upper winding as hereinbefore explained. Relay 27 also closes a holding circuit for relay 34 from conductor 51.

Relay 28 is disconnected from conductor 51 by relay 27, and thereupon falls back to disconnect relay 21. Although relay 21 remains connected in parallel with the upper winding of back-bridge relay 301 of the connector C1 until relay 28 falls back, relay 21 does not operate responsive to the closure of the bridge across conductors 50 and 52 on account of its relatively stiff adjustment.

The operation of back-bridgerelay 301 brings about the hereinbeore-described reversal of current flow in the talking conductors incoming to the connector C1, so as to give supervision over the calling end of the connection if desired.

The calling and called subscriber may now converse with each other as desired, and when the conversation has terminated they replace their receivers. Y

When the receiver is replaced at substation A1, the opening of the circuit of the transmitter battery 4 lowers the negative potential applied to the grid 34, with thc result that the current in the plate circuit of grid 35 is momentarily lowered as hereinbefore pointed out, resulting in the restoration of rela-y 26. When relay 26 restores, the circuit of back-bridge relay 301 is opened and relay 301 falls back and reverses the current flow in the incoming conductors back to normal.

When the receiver is replaced at substation A2, the selector S, the connector C1, and the calling lineswitch are released in the usual manner, and ground potential is removed from conductors 51 and 51. When this occurs, the circuit of relays 24 and 27 is opened, whereupon these relays fall back and the apparatus is in the normal condition shown in the drawings.

A local call on Zinc 10 The operations involved in the making of a local call between two subscribers on line 10 will now be explained. For this purpose it will be assumed that the subscriber at substation A1 desires to converse with another subscriber on the same line. In order to signal the other subscriber, the subscriber at substation A1 operates his hand generator 9 in accordance with the code assigned to the substation of the other subscriber. The first time the hand generator is operated, relays 22 and 23 in the repeater R operate as before described, and with the same results, and when relay 22 falls back, relays 25 and 24 are operated one after the other responsive to the momentary impulse transmitted to relay 25 through the contacts of relays 22 and 23. Following this momentary impulse, the armature spring of relay 25 vibrates in order to mantain relay 24 operated for an interval of time as hereinbefore explained. Under this condition, the filaments of the tubes 34 and 35 are lighted and plate current is supplied to the plate circuits of both tubes, but relay 26 is not operated because the calling subscriber has not removed his receiver. Under this condition, if special provisions were not made, plate relay 26 would follow the reversals of polarity imposed on line 10 during the second operation of the hand generator 9. In order to prevent this, relay 23 is arranged to interrupt the supply of plate current to the tubes 34 and 35 when it reoperates responsive to the reoperation of the AC relay 22 when the hand generator is next operated. This prevents needless operations of the automatic switching apparatus.

The subscriber at substation A1 continues to operate his hand generator in accordance with its successive rings in the code assigned to the desired substation, relays 22 and 23 reoperating responsive to each additional application of ringing current.

When the calling subscriber at substation Al removes his receiver to listen for the response of the called subscriber, the negative potential oi= the transmitter battery 4 at substation Al is impressed upon the grid element of tube 34, causing relay 26 to operate as before described. This results in the o'peration of the lineswitch LS to seize a first selector such as S, and the line l0 is guarded at this time by the hereinbefore described application of ground potential to conductor 51.

Using the repeater R n con-junction with a full-metallic Zine In order to explain how the repeater R operates when it is used in conjunction with a full-metallic line, it will be assumed that the line of substation Al is changed to a full metallic line. In this case the ground connection shown at substation A is removed and conductor 3 is extended to the exchange. Conductor 3 in this case connects to terminal 32 at the repeater R, and the ground connection is removed from the terminal 32. In order to provide a ground connection to Conductor 3 for the purpose of enabling the potential of the transmitter battery 4 to be properly impressed on the grid element of the tube 34, the upper terminal 33 of the lower lett-hand repeating-coil winding at the repeater R is grounded. lith the connections made as just described, the repeater R operates the same in connection v with a full-metallic line as described in connection with the single-conductor, groundreturn line.

Additional explanation,

Tt has been mentioned hereinbeiore in connection with the description of the operation of the system that the sending of the 100G-cycle current from the oscillator OS through the primary winding of the transformer 46, connected in circuit between the tubes 34 and 35, has a beneficial effect on the operation of relay 26. Attempts to account tor the somewhat more reliable response of relay 26 when the oscillator is in operation have been only partly successful. lt was at once discovered, by placing a milliammeter in series with relay 26, that the plate current is somewhat lower when the oscillator is in operation., this being` Yaccounted for by the tendency oi the tube 35 to respond diii'erently to the positive and negative impulses from the oscillator. The eliect of increasing the potential orn the biasing battery 49 slightly to secure the same iiow orP plate current without the oscillator GS being connected up was tried, and il, was found that the response ot relay 26 was for a time about as faithful as when the oscillator was employed. For some reason, however, for which no adequate ei;-

planation has been so far obtained, the operation ofrelay 26 seems to become less reliable after a few hours if the oscillator has not been in operation. For this reason it is concluded that the operation of the repeater B in making calls outgoing from the line l0 is more dependable when the oscillator OS is provided and connected as shown. Moreover, in many installations an oscillator may be required Jfor other pur-- nection to the transmitter battery such as the battery 4 at substation Al in order that the normal potential ot the grid of tube 34 be alteredin a negative direction upon the opening of the springs of the calling device and in a positive direction upon the closing of the springs of the calling device. It is considered, however, that the potential of the transmitter battery at substation A1 is insuiiicient to bring about the required alteration of grid potential at the tube 34 to permit a reliableresponse of relay 26 when connected in the plate circuit ot the tube. This objection, however, may be overcome by the selection of the proper tube. Another suggested method for overcoming this objection is to employ an additional battery at each substation. This battery at substation Al would be connected in series with the impulse contacts of the calling device CD, preferably between the. lower terminal of the calling device CD and the junction which conductor 2 makes with the upper terminal of the ringer 8. This arrangement, ot course, would require this additional battery at each substation on a party line and is considered to be less economical than the arrangement shown in connection with the. repeater R and employing the two tubes 34 and 35. Another point in favor of the arrangement shown and described is that the amplifying power of tube 34 is such that a sutcient actuating impulse is delivered from the plate of tube 34 to the grid oi tube 35 responsive to the openings and closings of the `impulse spring `of the calling device CD and the removals and replacements of the receiver 5 to secure the desired response of relay 26 even when the line l0 is very nearly completely grounded through contacts with the foliage of growing trees and the like. Therefore, since the normal iiow of current through relay 26 is in no way aiiected by the grounded or ungrounded condition of line 10, the

automatic switch having access to commonrelay continues to operate reliably as long as the received impulse is of sufficient strength, after amplification by tube 34:, to bring about the minimum required momentary change of plate current at the tube 35.

What is claimed is: Y

'1. In an automatic telephone system, means including a train of automatic switches controlled from a calling subscribers line for setting up a connection from the calling line to a called line responsive to series of impulses, a repeater individual to the calling line and interposed between the calling subscribers line and the train of switches, and a vacuum tube in said repeater arranged to respond to the impulses received over the calling subscribers line and to repeat them to the automatic switches.

2. In an automatic telephone exchange system, a subscribers line entering a telephone exchange, a line switch individual to said subscribers line and arranged to extend said line to exchange switching apparatus when a. call is made thereover, and an impulse repeater interposed between said line and the lineswitch, said repeater including vacuum-tube apparatus arranged to respond to impulses received from said line and to repeat them to the automatic exchange apparatus.

3. In an automatic telephone exchange system, an automatic telephone line entering an exchange, an impulse sender at a substation on said telephone line, a repeater individual to said line in the exchange, means in said repeater including vacuuin-tube apparatus responsive to the impulse sender on said line to repeat impulses to the exchange apparatus when a call is being made from said line, and means in said repeater for applying ringing current to said line when the line is called.

l4. In an automatic telephone system, an

battery lines and to local-batteryv lines, means for operating said switch to extend a connection to a line of either type, said switch having two wipers included in the talking connection set up to a line, means including a ringing relay in said automatic switch for applying ringing current to a called line through one of its said wipers and for applying direct current toa called line through the other of its said wipers, said ringing current being effective to directly signal the called substation in case a common-battery line is being called, and a ringing relay interposed between each localbattery line and said automatic switch, said ringing relay being responsive to the application of direct current through the said other wiper of said automatic switch to make a corresponding application of ringing current to the calledvv local-battery line.v

5. In an automatic telephone system, subscribers lines entering an automatic exchange, there being a repeater at the exchange interposed between each of said lines of the exchange apparatus, means in said repeater effective when a call is being made from the associated line for repeating switch-controlling impulses from the line to the exchange apparatus, and means in each repeater effective when a call is being made to the associated line for relaying ringing current from the exchange apparatus to the associated line, and means including a vacuum-tube in said repeater, controlled from the Vcalled line for terminating the ringing operationV when the called subscriber responds.

6. In an automatic telephone system, a subscribers line entering an automatic telephone exchange, means at the exchange responsive to an application of ringing current made over said subscribers line from a generator on the line to prepare a switchcontrol circuit, and means responsive to the removal of the receiver on the calling line for completing such switch-control circuit.

7. In an automatic telephone exchange system, automatic switches in an exchange arranged to respond to directive control to set up telephone connections, telephone lines entering said exchange, non-numerical switching apparatus arranged to effect a connection between a calling telephone line and one of said automatic switches, means responsive to the making of an application of ringing current from a source of ringing current at a calling substation for preparing to operate said non-numerical switching apparatus, and means responsive to the subsequent removal of the receiver at the calling substation for operating said non-nuinerical switching apparatus to extend a calling line to one of said automatic switches.

8. In an automatic telephone exchange system, automatic switches in a telephone exchange arranged to respond to directive control to set up telephone connections, telephone lines entering said exchange, nonnuinerical switching apparatus to effect a connection between. a calling telephone line and one of said automatic switches, means responsive to the making of an application oi ringing current from a source of ringing current at a calling substation for preparing to operate said non-numerical switching apparatus, means responsive to the subsequent removal of the receiver at the calling substation for operating said non-numerical switching apparatus to extend a calling line to one of said automatic switches, and means for automatically eifacing the said preparation in case the receiver is not removed at the calling substation before the lapse of a given interval of time.

' 9. In an automatic telephone exchange system, local-battery automatic-telephone lines entering the exchange, each telephone substation on one of said lines being provided with a local battery arranged to energize the transmitter' thereat, circuit arrangements for setting up a current tlow trom the local battery at a calling substation over the 'associated line to the automatic exchange, a

calling device at each local-battery substation arranged to interrupt the said current flow in accordance with the digits in the desired telephone numbers, and automatic switching apparatus in the exchange responsive to the interruptions ot the said current. flow to set up the desired connection.

l0. ln an autcniatic telephone system, a line over which automatic switches are to be controlled, an impulse repeater inserted in said line, means :tor preparing a switchcontrol circuit at said repeater responsive to an application of ringing current and for completing said switch-control circuit a'lter the application of ringing current is terminated, means tor transmitting switch-controlling impulses to said repeater, said repeater being effective to repeat said switch controlling impulses into the said switchcontrol circuit, and means responsive to an additional application of ringing current tor opening the said switch-control circuit tor the duration of such application in order to prevent the repeating of erroneous switchcontrolling impulses.

ll. In an impulse repeater for use m an automatic telephone system to repeat switchoperatinv impulses to automatic-switching apparatus, a vacuum tube having a plate circuit, a current source connected in said plate circuit to drive current therethrough, a. repeating relay connected in said plate circuit and having contacts thereon arranged to repeat said switch-controlling impulses, the plate current in said plate circuit being adjusted with respect to the characteristics ot said repeating relay to such a value that the repeating relay will not respond to the normal tlow ot' plate current but will respond in case the normal flow of' plate current is momentarily increased and will then remain operated by the normal low ot plate current, means for sending a momentary impulse to the grid element of said vacuum tube of such a polarity as to cause a momentary increase in the flow of plate current therethrough to operate said repeating relay to close said switch-control circuit and prepare the automatic switching apparatus tor operation, and means tor subsequently sending a series of impulses to the grid element of said vacuum tube of the two polarities alternately so that the plate current is alternately decreased below its normal value and increased above its normal value, said repeating relay being responsive to each decrease in the plate current to restore and open the switch-control circuit and responsive to each increase in the flow of plate current to operate and again close the switch-control circuit.

12. In an impulse repeater for use in an automatic telephone system to control the operation of automatic switches, an impulse repeating relay and means tor sending a current therethrough insufficient to operate it but suiiicient to hold it operated, and means controlled by an impulse sender on a calling subscribers line tor alternately increasing and decreasing the current-flow through the relay to secure'its alterna-te operation and restoration.

13. ln an impulse repeater for use in an automatic telephone system to control the operation ot automatic switches, an impulse repeating relay and` means tor sending a current therethrough insuiiicient to operate it but sufficient to hold it operated, and means controlled by an impulse sender on a calling subscribers line for alternately increasing and decreasing the current-flow through the relay to secure its alternate operation and restoration, said means including a vacuum-tube ampliiier interposed between said line and said relay.

141. ln an impulse repeater, a vacuiun tube having a grid element and a plate circuit, said plate circuit including a current source and a repeating relay, the current-flow in said plate circuit being insuiiicient to operate said relay but suiiicient to maintain it operated, and means for sending impulses to the grid element or" said tube to cause said current flow to alternately increase and decrease so as to cause said relay to operate and restore.

15. In an impulse repeater, a vacuum tube having a grid element and a` plate circuit, said plate circuit including a current source and a repeating relay,l the current-flow in said plate circuit being insui'licient to operate said relay but suiiicient to maintain it operated, means for sending impulses to the grid element of said tube to cause said current flow to alternately increase and decrease so as to cause said relay to operate and restore, and an additional vacuum tube interposed between said means and the firstnamed tube.

1G. In an impulse repeater, a vacuum tube having a grid element and having a plate circuit having a current dow therein controlled by potentials impressed on the grid element, a repeating relay included in said plate circuit and responsive to current-Flow variations, means for impressing direct-current potentials on the grid element to control the operation ot said repeating relay, and means tor continuously impressing an alternating current potential on said grid element to improve the response of said repeating relay and render it more reliable.

l so

17. In an automatic telephone system,"an exchange including automatic switching apparatus arranged to respond to impulsesto set up telephone connections between the lines of the exchange; single-conductor ground-return rural lines entering said eX- change; and means including vacuum-tube impulse repeaters for enabling the automa tic switching apparatus to be controlled from said rural lines.

18. In a telephone system, a telephone line having a vacuum tube connected thereto, means for impressing ringing current on said telephone line and for removing said vacuum tube from under the control of said line While ringing current is being impressed, and means for draining the residual ringing current from said line before again placing said vacuum tube under the control thereof. p

19; In a telephone system, a telephone line, a vacuum tube connected to said line and arranged to be controlled thereover, means for making an. application of ringing current to said line and for disabling the vacuum tube from operating under the control of said line during suchapplication, and means for momentarily grounding said line at the termination of the application of ringing current to remove the residual ringing current from the line and thereby pre vent a false control being exercised over the vacuum tube.

20. In a telephone system, a grounded subscribers line, a battery connected between the line and ground at the subscribers station, a calling device for interrupting the said connection in accordance With digits in called numbers, and a repeater-at the eX- change, said repeater including a vacuum tube having its grid connected to said line, and repeating means controlled by the plate circuit of said tube.

v 21. In combination, a subscribers line, a repeater at the exchange including a vacuum tube having its grid connected to said line, means in said repeater for normally maintaining a vpositive potential on said grid, means including a battery at the subscribers station for placing a negative potential on the line and on said grid When the line is closed at said station, a calling device for interrupting the battery circuit at said station in. accordance with digits in called numbers, thereby intermittently restoring ythe positive potential on said grid, and impulse repeating means controlled over the plate circuit of said tube responsive to current changes produced by the operation of said calling device.

In Witness whereof, I hereunto subscribe my name this 21st day of October, A. D.

CHARLES R. BROOKS. 

